From the scientific and patent literature it is known that it is possible to copolymerize propylene with 1,3-butadiene, in the presence of Ziegler-Natta catalysts, to obtain alternated or random copolymers.
It is known as well that the products so obtained contain butadiene units whose configuration is always prevailing of the 1,4-cis or trans type (see for example W. Cooper in "The Stereo Rubbers", Saltman ed., John Wiley & Sohns, New York 1977 and annexed quotations). These materials, because of their having the double bond inserted in the main chain, are easily subject to thermal degradation and even more to oxidative degradation.
Therefore, from the viewpoint of the product stability it would be of great interest to obtain copolymers having the butadiene linked in configuration 1,2 and, by consequence, the double bond in the side chain.
In fact it is known that the vinyl-type unsaturations give rise to scission.
Furthermore, according to the art, the copolymerization of propylene with butadiene must be accomplished at very low temperatures, generally below 0.degree. C., and the catalytic activity is only corresponding to a few grams of polymer per gram of titanium.